Greek traders said on Sunday they expected a torrid day of losses when the Athens stock market opens after being shuttered for five weeks as part of attempts to stop Greece's financial collapse.
A combination of pent-up trading, worries about the future and Greece's worsening economy could knock 20 percent or more off the Athens General Index on Monday, they said.
Trading of Greek assets in the United States over the period the bourse has been closed suggests the same.
"The possibility of seeing even a single share rise in [Monday's] session is almost zero," said Takis Zamanis, chief trader at Beta Securities.
The stock market is due to open on Monday morning for the first time since June 26, just before capital controls were imposed to stem a flight of euros.
This was the result of the failure of Greece and its European Union and International Monetary Fund creditors to agree a new cash-for-reforms deal.
Since then, a deal has been reached, but its implementation may prove hard and political in-fighting in Athens over the bailout rules could prompt a new election.
"There is a lot of uncertainty about the government's ability to sign the ... bailout on time and for possible snap elections," Zamanis said.
Greece's economy has also begun to reverse the gains it was making before Prime Minister Alexis Tsipras was elected on a strong anti-austerity platform.
The European Commission predicts Greece will fall back into recession in 2015, contracting 2 to 4 percent after having only just emerged from a six-year downturn.
Banking stocks may take much of the brunt on Monday because Greece's financial sector needs to be recapitalised. A report in Sunday's Avgi newspaper, which is close to Tsipras' government, suggested Athens is seeking around 10 billion euros this month for bank recapitalization.
Banks constitute around 20 percent of the main Athens index. National Bank of Greece's US-listed stock has lost around 20 percent while the Athens bourse has been closed.
"The focus will be in the bank shares. They will suffer more because their investors have to face a dilution from the (expected) recapitalization of the sector," said one asset manager at a Greek fund.
He added that Greek banks will not be profitable this year and are suffering from an increase in bad loans due to the crisis. "It would be realistic to expect a decline of about 15- 20 percent (at) the opening of the market on Monday," the asset manager said.